Pop stash instead of applying

The `pop` was changed to `apply` in 8683da4a as a safety measure while
issue #55 was tracked down. The root cause was fixed in 205c0b46 and
released in v0.13.0. We should restore previous behavior so that the
stash is useful again.

Fixes #62.

Change-Id: I3d243accf80334323299bd19b71b1e295ef9cf9a
Reviewed-on: http://gerrit.causes.com/40371
Tested-by: jenkins <jenkins@causes.com>
Reviewed-by: Shane da Silva <shane.dasilva@brigade.com>