Description of problem:
If User provides invalid string instead of absolute path name of configuration
file in '-c' option then ipa command throws traceback. Error message given by
command is useful but traceback is too loud.


# ipa -c non_existent_file_name
[2016-07-18T11:59:25Z ipa] <ERROR>: ValueError: config_file must be an absolute
path; got u'non_existent_file_name'
Traceback (most recent call last):
  File "/usr/lib/python2.7/site-packages/ipalib/cli.py", line 1333, in run
    (options, argv) = api.bootstrap_with_global_options(context='cli')
  File "/usr/lib/python2.7/site-packages/ipalib/plugable.py", line 514, in
bootstrap_with_global_options
    self.bootstrap(parser, **overrides)
  File "/usr/lib/python2.7/site-packages/ipalib/plugable.py", line 379, in
bootstrap
    self.env._finalize_core(**dict(DEFAULT_CONFIG))
  File "/usr/lib/python2.7/site-packages/ipalib/config.py", line 532, in
_finalize_core
    self._merge_from_file(self.conf)
  File "/usr/lib/python2.7/site-packages/ipalib/config.py", line 367, in
_merge_from_file
    'config_file must be an absolute path; got %r' % config_file
ValueError: config_file must be an absolute path; got u'non_existent_file_name'
[2016-07-18T11:59:25Z ipa] <ERROR>: an internal error has occurred


Version-Release number of selected component (if applicable):
ipa-server-4.4.0-1.el7.x86_64

How reproducible:
100%

Steps to Reproduce:
1. ipa -c non_existent_file_name

Actual results:
Error message with traceback.

Expected results:
Error message is correct but traceback is undesirable to user.