customization: ask for admin password

admin password was hardcoded, now it is asked at
customization stage.
Also avoid to fail the setup if the only missing step
is adding the local host to the datacenter (for example
for wrong password)

Change-Id: I62d1e93ae6ff4a5eb32b243b2f846121ea84595c
Signed-off-by: Sandro Bonazzola <sbonazzo@redhat.com>