failed apache-hive installs should fail well

[Kevin W Monroe]

Hive was broken for a bit. Sam deployed it and had a failed installation. We fixed it, and he tried a juju upgrade-charm to get the new bits. Unfortunately, we don't handle partial installation very well at all. Since the first install failed, we never set the hive.installed KV, and upgrade-charm re-entered the install->setup_hive_config. This broke as this log snippet shows:

unit-hive-0[11112]: 2015-09-01 09:37:30 INFO unit.hive/0.hadoop-plugin-relation-changed logger.go:40 File "/var/lib/juju/agents/unit-hive-0/charm/hooks/callbacks.py", line 81, in install
unit-hive-0[11112]: 2015-09-01 09:37:30 INFO unit.hive/0.hadoop-plugin-relation-changed logger.go:40 self.setup_hive_config()
unit-hive-0[11112]: 2015-09-01 09:37:30 INFO unit.hive/0.hadoop-plugin-relation-changed logger.go:40 File "/var/lib/juju/agents/unit-hive-0/charm/hooks/callbacks.py", line 97, in setup_hive_config
unit-hive-0[11112]: 2015-09-01 09:37:30 INFO unit.hive/0.hadoop-plugin-relation-changed logger.go:40 default_conf.copytree(hive_conf)
unit-hive-0[11112]: 2015-09-01 09:37:30 INFO unit.hive/0.hadoop-plugin-relation-changed logger.go:40 File "/usr/lib/python2.7/shutil.py", line 171, in copytree
unit-hive-0[11112]: 2015-09-01 09:37:30 INFO unit.hive/0.hadoop-plugin-relation-changed logger.go:40 names = os.listdir(src)
unit-hive-0[11112]: 2015-09-01 09:37:30 INFO unit.hive/0.hadoop-plugin-relation-changed logger.go:40 OSError: [Errno 2] No such file or directory: '/usr/lib/hive/conf'

Couple options to fix this:
1. test for, or try/except around, actions on the /usr/lib/hive/conf directory
2. blow away hive-related filesystem changes in the beginning of install, and let install set it all back up again.