Fix implementation of rc variables $amd_flags and $amd_map_program in

Fix implementation of rc variables $amd_flags and $amd_map_program in
rcNG. The $amd_flags variable was already taken over into $rc_flags
by run_rc_command() when amd_precmd() is executed, so changing
$amd_flags there no longer effects the actual execution of amd.
Hence in amd_precmd() the $rc_flags have to be adjusted instead.