Helper to file bugreports

[jonasstein]

Similar to #113
it would be nice to have a tool, which collects the data for failed builds

sketch:

pkgbug --reportbuildfail "/app-shells/bash-1.2.3"

<runs emerge, if emerge works break>
<opens $EDITOR>
Subject: /app-shells/bash-1.2.3: Build fails
<empty line as known in git>
# write your report here
#
emerge info:
------8<-------------------
....
# end of comment

INFO: bug report created https://bugs.gentoo.org/12345
INFO: build.log was successfully attached 

Should this go into a new script like pkgbug, or should it be an extension of pkgcheck?