ami_install: use separate file for stderr

Both outputs were stomping on each other in the log file.

Signed-off-by: Pierre-Alexandre Meyer <pierre@mouraf.org>
ami_install: fixes around aptitude

* Tell it that we're not using a real terminal
* update after the safe-upgrade to work around non-deterministic behaviors

Signed-off-by: Pierre-Alexandre Meyer <pierre@mouraf.org>
ami_install: trivial fixes in install_tomcat_from_targz

Signed-off-by: Pierre-Alexandre Meyer <pierre@mouraf.org>