frome: Install bash, needed by ssl-cert

The make-ssl-cert script specifically targets bash, so let's install it explicitly.

The ssl-cert package is brought in by postfix, which is needed by quilt, suggested by devscript.

This fixes the error below:

Setting up ssl-cert (1.0.39ba1) ...
/var/lib/dpkg/info/ssl-cert.postinst: 48: /var/lib/dpkg/info/ssl-cert.postinst: make-ssl-cert: not found
dpkg: error processing package ssl-cert (--configure):
 installed ssl-cert package post-installation script subprocess returned error exit status 127

The install error also caused the subsequent tests to be skipped due to the inconsistent state.