test: Create and set temporary home directory

In the master branch in test/emacs two tests access the build users home
directory, so does emacs_deliver_message in the crypto branch.

The tests should not touch the build user's home directory. The patch
creates a directory in the temporary test directory and sets home
accordingly.

In case of a non-existent home directory, the tests are failing without
this patch.

Signed-off-by: Jameson Graef Rollins <jrollins@finestructure.net>