Description of problem:

Online Backup is failing when --incremental is specified


Version-Release number of selected component (if applicable):

satellite-6.3.0-1.0.git.7.fb12bf2.el7sat.noarch

How reproducible:

6.3.z

Steps to Reproduce:

Create a backup using `--online-backup`

$katello-backup /tmp/b1_dir2 --online-backup 
Starting backup: 2016-10-31 20:14:24 +0100
Creating backup folder /tmp/b1_dir2
Backing up config files... 
tar: Removing leading `/' from member names
Done.
Backing up postgres db... 
Done.
Backing up mongo db... 
Done.
Backing up Pulp data... 
tar: Removing leading `/' from member names
Done.
Done with backup: 2016-10-31 20:14:26 +0100
**** BACKUP Complete, contents can be found in: /tmp/b1_dir2 ****

# perform some changes in the system, create product, repo etc (actually error happens even if nothing is changed)


# Try to run incremental online backup in the same folder

$katello-backup /tmp/b1_dir2 --online-backup --incremental
/usr/bin/katello-backup:17:in `exist?': no implicit conversion of nil into String (TypeError)
	from /usr/bin/katello-backup:17:in `block (2 levels) in <main>'
	from /usr/share/ruby/optparse.rb:1364:in `call'
	from /usr/share/ruby/optparse.rb:1364:in `block in parse_in_order'
	from /usr/share/ruby/optparse.rb:1351:in `catch'
	from /usr/share/ruby/optparse.rb:1351:in `parse_in_order'
	from /usr/share/ruby/optparse.rb:1345:in `order!'
	from /usr/share/ruby/optparse.rb:1437:in `permute!'
	from /usr/share/ruby/optparse.rb:1459:in `parse!'
	from /usr/bin/katello-backup:29:in `block in <main>'
	from /usr/share/ruby/optparse.rb:885:in `initialize'
	from /usr/bin/katello-backup:9:in `new'
	from /usr/bin/katello-backup:9:in `<main>'

$ echo $?
1


Actual results:

/usr/bin/katello-backup:17:in `exist?': no implicit conversion of nil into String (TypeError)

Expected results:

Existing backup would be incremented

Additional info:

satellite-6.3.0-1.0.git.7.fb12bf2.el7sat.noarch