Support: --macrofile=<file>...

This allow us to put --define... in a --macrofile,
and let it be added to %topdir/SPECS/
which specfiles can include.
Run spectool before yum-builddep step.
Throw PackagerException is image is none.
Tests for PackagerContext.
Merge pull request #13 from norrs/packager_context_tests

Packager context tests
Merge pull request #7 from norrs/macrofile

Support --macrofile...
Removing real file from config tests
Adding tox testing for py27 and py34 with coverage reports
Tests for rpmbuild packager classes