Devstack can't build because python-troveclient is missing

[Mahito OGURA]

python-troveclient can't pass to the gate test because Devstack can't build.
Log is as follow.

```
2017-10-22 22:56:06.652 | + ./stack.sh:main:1392 : check_libs_from_git
2017-10-22 22:56:06.654 | + inc/python:check_libs_from_git:428 : local lib=
2017-10-22 22:56:06.656 | + inc/python:check_libs_from_git:429 : local not_installed=
2017-10-22 22:56:06.659 | ++ inc/python:check_libs_from_git:430 : tr , ' '
2017-10-22 22:56:06.661 | ++ inc/python:check_libs_from_git:430 : echo python-troveclient
2017-10-22 22:56:06.665 | + inc/python:check_libs_from_git:430 : for lib in '$(echo ${LIBS_FROM_GIT} | tr "," " ")'
2017-10-22 22:56:06.667 | + inc/python:check_libs_from_git:431 : lib_installed_from_git python-troveclient
2017-10-22 22:56:06.669 | + inc/python:lib_installed_from_git:408 : local name=python-troveclient
2017-10-22 22:56:06.672 | + inc/python:lib_installed_from_git:422 : pip list
2017-10-22 22:56:06.672 | + inc/python:lib_installed_from_git:422 : grep -- python-troveclient
2017-10-22 22:56:06.674 | + inc/python:lib_installed_from_git:422 : grep -q -- ', .*)$'
2017-10-22 22:56:07.697 | + inc/python:check_libs_from_git:432 : not_installed+=' python-troveclient'
2017-10-22 22:56:07.699 | + inc/python:check_libs_from_git:436 : [[ -n python-troveclient ]]
2017-10-22 22:56:07.701 | + inc/python:check_libs_from_git:437 : die 437 'The following LIBS_FROM_GIT were not installed correct: python-troveclient'
2017-10-22 22:56:07.703 | + functions-common:die:187 : local exitcode=0
2017-10-22 22:56:07.705 | [Call Trace]
2017-10-22 22:56:07.706 | ./stack.sh:1392:check_libs_from_git
2017-10-22 22:56:07.706 | /opt/stack/new/devstack/inc/python:437:die
2017-10-22 22:56:07.709 | [ERROR] /opt/stack/new/devstack/inc/python:437 The following LIBS_FROM_GIT were not installed correct: python-troveclient
2017-10-22 22:56:08.714 | Error on exit
```

http://logs.openstack.org/91/455591/2/check/legacy-tempest-dsvm-neutron-src/ceebbd8/logs/devstacklog.txt.gz#_2017-10-22_22_56_07_709

[Mahito OGURA (earthdragon77)]

This problem seems to be the cause of this patch
https://review.openstack.org/#/c/508366/