Before installing ansible using "pip install -U ansible" , we need to install following packages 
ubuntu : python-dev , libssl-dev , gcc 
Centos : python-devel, openssl-devel, gcc

For ubuntu: if python-dev not installed then Error will be : 

    writing requirements to src/cryptography.egg-info/requires.txt
    writing src/cryptography.egg-info/PKG-INFO
    writing top-level names to src/cryptography.egg-info/top_level.txt
    writing dependency_links to src/cryptography.egg-info/dependency_links.txt
    writing entry points to src/cryptography.egg-info/entry_points.txt
    warning: manifest_maker: standard file '-c' not found
    
    reading manifest file 'src/cryptography.egg-info/SOURCES.txt'
    reading manifest template 'MANIFEST.in'
    no previously-included directories found matching 'docs/_build'
    warning: no previously-included files matching '*' found under directory 'vectors'
    writing manifest file 'src/cryptography.egg-info/SOURCES.txt'
    running build_ext
    generating cffi module 'build/temp.linux-x86_64-2.7/_padding.c'
    creating build/temp.linux-x86_64-2.7
    generating cffi module 'build/temp.linux-x86_64-2.7/_constant_time.c'
    generating cffi module 'build/temp.linux-x86_64-2.7/_openssl.c'
    building '_openssl' extension
    creating build/temp.linux-x86_64-2.7/build
    creating build/temp.linux-x86_64-2.7/build/temp.linux-x86_64-2.7
    x86_64-linux-gnu-gcc -pthread -fno-strict-aliasing -DNDEBUG -g -fwrapv -O2 -Wall -Wstrict-prototypes -fPIC -I/usr/include/python2.7 -c build/temp.linux-x86_64-2.7/_openssl.c -o build/temp.linux-x86_64-2.7/build/temp.linux-x86_64-2.7/_openssl.o
    build/temp.linux-x86_64-2.7/_openssl.c:12:24: fatal error: pyconfig.h: No such file or directory
     #  include <pyconfig.h>
                            ^
    compilation terminated.
    error: command 'x86_64-linux-gnu-gcc' failed with exit status 1
    
    ----------------------------------------
Command "/usr/bin/python -u -c "import setuptools, tokenize;__file__='/tmp/pip-build-HDDNRD/cryptography/setup.py';exec(compile(getattr(tokenize, 'open', open)(__file__).read().replace('\r\n', '\n'), __file__, 'exec'))" install --record /tmp/pip-RmBIw5-record/install-record.txt --single-version-externally-managed --compile" failed with error code 1 in /tmp/pip-build-HDDNRD/cryptography/
/usr/local/lib/python2.7/dist-packages/pip/_vendor/requests/packages/urllib3/util/ssl_.py:122: InsecurePlatformWarning: A true SSLContext object is not available. This prevents urllib3 from configuring SSL appropriately and may cause certain SSL connections to fail. You can upgrade to a newer version of Python to solve this. For more information, see https://urllib3.readthedocs.org/en/latest/security.html#insecureplatformwarning.
  InsecurePlatformWarning








after installing python-dev below error will occur : 

    generating cffi module 'build/temp.linux-x86_64-2.7/_constant_time.c'
    generating cffi module 'build/temp.linux-x86_64-2.7/_openssl.c'
    building '_openssl' extension
    creating build/temp.linux-x86_64-2.7/build
    creating build/temp.linux-x86_64-2.7/build/temp.linux-x86_64-2.7
    x86_64-linux-gnu-gcc -pthread -fno-strict-aliasing -DNDEBUG -g -fwrapv -O2 -Wall -Wstrict-prototypes -fPIC -I/usr/include/python2.7 -c build/temp.linux-x86_64-2.7/_openssl.c -o build/temp.linux-x86_64-2.7/build/temp.linux-x86_64-2.7/_openssl.o
    build/temp.linux-x86_64-2.7/_openssl.c:433:30: fatal error: openssl/opensslv.h: No such file or directory
     #include <openssl/opensslv.h>
                                  ^
    compilation terminated.
    error: command 'x86_64-linux-gnu-gcc' failed with exit status 1
    
    ----------------------------------------
Command "/usr/bin/python -u -c "import setuptools, tokenize;__file__='/tmp/pip-build-ZN2RG3/cryptography/setup.py';exec(compile(getattr(tokenize, 'open', open)(__file__).read().replace('\r\n', '\n'), __file__, 'exec'))" install --record /tmp/pip-akw7P8-record/install-record.txt --single-version-externally-managed --compile" failed with error code 1 in /tmp/pip-build-ZN2RG3/cryptography/
/usr/local/lib/python2.7/dist-packages/pip/_vendor/requests/packages/urllib3/util/ssl_.py:122: InsecurePlatformWarning: A true SSLContext object is not available. This prevents urllib3 from configuring SSL appropriately and may cause certain SSL connections to fail. You can upgrade to a newer version of Python to solve this. For more information, see https://urllib3.readthedocs.org/en/latest/security.html#insecureplatformwarning.
  InsecurePlatformWarning



For above error i installed libssl-dev. 

then problem solved