Move try: cfg.get excepts to CephConfg.safe_get

move safe_get from config to conf.CephConfig
update existing uses of safe_get
move try: ... except to cfg.safe_get
remove not needed imports

Signed-off-by: Andrew Woodward (awoodward@mirantis.com)
Update catch_mon_errors and tests

change mon_initial_members test in mon.catch_mon_errors to be able to catch
 None result correctly
add second test to test_mon to ensure both None and not hostname in ..
 are tested

Signed-off-by: Andrew Woodward (awoodward@mirantis.com)
Merge pull request #91 from xarses/6369-xarses

Move cfg.get try/excepts to safe_git