qubes.py: postpone qmmeman.close()
qubes.py: postpone qmmeman.close()

There are indications that when parent "xl" process exits, the domain is not
booted completely; and xl actions may interfere with qmemman memory balancing.
Thus, in VM.start(), we delay releasing of qmemman handle until qrexec_daemon
connects successfully.

woju/qubes-core-admin,woju/qubes-core-admin,QubesOS/qubes-core-admin,marmarek/qubes-core-admin,woju/qubes-core-admin,woju/qubes-core-admin,marmarek/qubes-core-admin,QubesOS/qubes-core-admin,marmarek/qubes-core-admin,QubesOS/qubes-core-admin