Add a ks_meta variable "remote_post"

Using this variable, a remote script can be specified which will be
executed post installtion. The remote script must have an appropriate #!
line to indicate the script interpreter.

Bug: 1099231
Change-Id: I17532d6bf71223282c386fb332108644b30586df
Remove the "exit 0" in remote_post to work around possible RHEL 6 bug

This was introduiced in 1479a07
Include remote_post before reporting postinstall_done

(The original patch introduced this in 1479a07)

Bug: 1099231