MFT: Injail pkg invocations related to cachedir.
This makes it possible to build pkgng packages from a host without pkg installed.
Also, this makes possible to use custom LOCALBASE (/usr/sbin/pkg from the host was
using the LOCALBASE environment variable which led to interesting problems when
LOCALBASE of the host was different from LOCALBASE in the jails)
MFT: Mount CCACHE_DIR in /root/.ccache as not all ports pass MAKE_ENV into the build.
MFT: jail: Fix cleanup and -d when using USE_TMPFS=all