lxc-alpine: download a static package manager if its missing

If the package manager, apk-tools is missing, then:
 - download a static binary and public keys
 - verify the keys against embedded checksum
 - verify the signature of the static binary against the downloaded keys
 - use the verified static binary

Signed-off-by: Natanael Copa <ncopa@alpinelinux.org>
Signed-off-by: Kaarle Ritvanen <kaarle.ritvanen@datakunkku.fi>
Signed-off-by: Serge Hallyn <serge.hallyn@ubuntu.com>
lxcapi_create: don't close stdin/out/err

Otherwise we can't see template progress.

Signed-off-by: Serge Hallyn <serge.hallyn@ubuntu.com>