yum will fail with a traceback if there is an empty line int he environment group file

Issue

• If there is a blank line in the /var/lib/yum/groups/environment file, yum will fail with a traceback:

[root@pmg-rhel7 ~]# vi /var/lib/yum/groups/environment 
[root@pmg-rhel7 ~]# yum group info SAP
Loaded plugins: product-id, subscription-manager
Traceback (most recent call last):
  File "/usr/bin/yum", line 29, in <module>
    yummain.user_main(sys.argv[1:], exit_code=True)
  File "/usr/share/yum-cli/yummain.py", line 367, in user_main
    errcode = main(args)
  File "/usr/share/yum-cli/yummain.py", line 160, in main
    base.getOptionsConfig(args)
  File "/usr/share/yum-cli/cli.py", line 352, in getOptionsConfig
    self.parseCommands() # before we return check over the base command + args
  File "/usr/share/yum-cli/cli.py", line 396, in parseCommands
    self.yum_cli_commands[self.basecmd].doCheck(self, self.basecmd, self.extcmds)
  File "/usr/share/yum-cli/yumcommands.py", line 1011, in doCheck
    elif not os.path.exists(os.path.dirname(base.igroups.filename)):
  File "/usr/lib/python2.7/site-packages/yum/__init__.py", line 1111, in <lambda>
    igroups = property(fget=lambda self: self._getIGroups(),
  File "/usr/lib/python2.7/site-packages/yum/__init__.py", line 1071, in _getIGroups
    self._igroups = yum.igroups.InstalledGroups(db_path=pdb_path)
  File "/usr/lib/python2.7/site-packages/yum/igroups.py", line 103, in __init__
    self._read_grp_grps(db_path)
  File "/usr/lib/python2.7/site-packages/yum/igroups.py", line 143, in _read_grp_grps
    groups_num = int(_read_str(fo))
ValueError: invalid literal for int() with base 10: ''
[root@pmg-rhel7 ~]#