pennyworth import-base-image breaks if local import-state.yml is empty

[greygoo]

Description:

running
pennyworth import-base-image --url http://machintegration.suse.de/machinery-internal/
failed with

-----------snip----------
undefined method []' for false:FalseClass /usr/src/chuller/pennyworth/lib/cli.rb:109:inexit'
/usr/src/chuller/pennyworth/lib/cli.rb:109:in rescue in import_base' /usr/src/chuller/pennyworth/lib/cli.rb:84:inimport_base'
/usr/lib64/ruby/gems/2.0.0/gems/thor-0.19.1/lib/thor/command.rb:27:in run' /usr/lib64/ruby/gems/2.0.0/gems/thor-0.19.1/lib/thor/invocation.rb:126:ininvoke_command'
/usr/lib64/ruby/gems/2.0.0/gems/thor-0.19.1/lib/thor.rb:359:in dispatch' /usr/lib64/ruby/gems/2.0.0/gems/thor-0.19.1/lib/thor/base.rb:440:instart'
/usr/src/chuller/pennyworth/bin/pennyworth:61:in <top (required)>' /usr/lib64/ruby/gems/2.0.0/gems/debugger-1.6.8/bin/rdebug:124:indebug_load'
/usr/lib64/ruby/gems/2.0.0/gems/debugger-1.6.8/bin/rdebug:124:in debug_program' /usr/lib64/ruby/gems/2.0.0/gems/debugger-1.6.8/bin/rdebug:394:in<top (required)>'
/usr/bin/rdebug2.0:23:in load' /usr/bin/rdebug2.0:23:in

'
Uncaught exception: exit
-----------snip----------

Upon debugging and further inspection it turned out that the local import-state.yml file was just an empty file which triggered this problem.

Removing the local import-state.yml worked around the problem, but we should check if that file is empty before reading and processing it further.