Merge lp://qastaging/~zyga/snapcraft/fix-1484596 into lp://qastaging/~snappy-dev/snapcraft/core

The attempt to merge lp:~zyga/snapcraft/fix-1484596 into lp:snapcraft failed. Below is the output from the failed tests.

The project has gotten complex.
Here's the list of units exceeding 10:
- snapcraft/cmds.py:
  286:1: 'cmd' 13

name: # the name of the snap
version: # the version of the snap
# The vendor for the snap (replace 'Vendor <email address hidden>')
vendor: Vendor <email address hidden>
summary: # 79 char long summary
description: # A longer description for the snap
icon: # A path to an icon for the package
cp --preserve=all -R zzz /tmp/tmpt5q9u6jg/parts/copy/install/zzz
cp --preserve=all -R src /tmp/tmpy68neff7/parts/copy/install/dst
cp --preserve=all -R src /tmp/tmpjtly1d6n/parts/copy/install/dir/dst
===============================[ Analyzing Jobs ]===============================
=============================[ Session Statistics ]=============================
This session is about 0.00% complete
Estimated duration is 0.10 for automated jobs.
Estimated duration cannot be determined for manual jobs.
Size of the desired job list: 27
Size of the effective execution plan: 27
===========================[ Running Selected Jobs ]============================
--------------[ Running job 1 / 27. Estimated time left: unknown ]--------------
--------------------------[ snapcraft/normal/no-yaml ]--------------------------
ID: 2015.com.canonical.snapcraft::snapcraft/normal/no-yaml
Category: 2013.com.canonical.plainbox::uncategorised

...................................Warning: unable to find "test_relexepath" in the path
...................................................................
----------------------------------------------------------------------
Ran 102 tests in 2.738s

OK
CRITICAL plainbox.crashes: Executable 'plainbox' invoked with Namespace(color=None, command=<plainbox.impl.commands.cmd_run.RunCommand object at 0x7ff0e61a1438>, debug_console=False, debug_interrupt=False, dont_suppress_output=False, dry_run=False, exclude_pattern_list=[], include_pattern_list=[], log_level=None, non_interactive=False, output_file=<_io.BufferedWriter name='/tmp/tmp.1vH2ytGhgO/result.json'>, output_format='json', output_options='', pdb=False, test_plan='2015.com.canonical.snapcraft::normal', trace=[], transport=None, transport_options=None, transport_where=None, whitelist=[]) has crashed
Traceback (most recent call last):
  File "/usr/lib/python3/dist-packages/plainbox/impl/clitools.py", line 560, in dispatch_and_catch_exceptions
    return self.dispatch_command(ns)
  File "/usr/lib/python3/dist-packages/plainbox/impl/clitools.py", line 556, in dispatch_command
    return ns.command.invoked(ns)
  File "/usr/lib/python3/dist-packages/plainbox/impl/commands/cmd_run.py", line 44, in invoked
    self.provider_loader, self.config_loader, ns, ns.color).run()
  File "/usr/lib/python3/dist-packages/plainbox/impl/commands/inv_run.py", line 356, in run
    return self.do_normal_sequence()
  File "/usr/lib/python3/dist-packages/plainbox/impl/commands/inv_run.py", line 410, in do_normal_sequence
    self.run_all_selected_jobs()
  File "/usr/lib/python3/dist-packages/plainbox/impl/commands/inv_run.py", line 740, in run_all_selected_jobs
    self.run_sin...

Rebased and pushed.