[WIP] Don't include static libraries in mysql images

[pshem]

Static libraries have been removed from mysql images. This speeds up the build process and shrinks the resulting image. All credit for the idea to @wkozaczuk, based on #64 (comment)

This should shrink MySQL images by ~45 Mb:

osv$ find apps/mysql/install/ -name '*.a' -exec du -h '{}' +
39M apps/mysql/install/usr/lib/libmysqld.a
0 apps/mysql/install/usr/lib/libmysqlclient_r.a
8.0K apps/mysql/install/usr/lib/libmysqlservices.a
6.3M apps/mysql/install/usr/lib/libmysqlclient.a

[pshem]

The image with static libraries is 53Mb, without them it's 35Mb.

However, I've discovered that this patch doesn't work:

• Running find apps/mysql/install/ -name '*.a' -exec rm '{}' + works and keeps the images shrunk until running make clean.
• Putting find $ROOTDIR -name '*.a' -exec rm '{}' + at the end of GET doesn't. I'll update the patch when I figure it out.