Use auto-alias for glance-manage

The current snaps now have well-known aliases defined at install time
for commands [1]. This means we can drop the manual alias definition
from snapcraft.yaml and the instructions for setting it up.

When building/installing locally users can still create the alias
with 'snap alias'.

[1] https://forum.snapcraft.io/t/auto-aliases-for-openstack-base-snaps/1146/6

Change-Id: Ib34183ded789775fa76d701bd78a168bccb5fa08

README.md

@@ -62,14 +62,6 @@ add those to $SNAP_COMMON as well.
 The services for the glance snap will log to its $SNAP_COMMON writable area:
 /var/snap/glance/common/log.
 
-## Managing glance
-
-The glance snap has alias support that enables use of the well-known
-glance-manage command. To enable the alias, run the following prior to
-using the command:
-
-    sudo snap alias glance.manage glance-manage
-
 ## Restarting glance services
 
 To restart all glance services:

snapcraft.yaml

@@ -23,8 +23,6 @@ apps:
       - network-bind
   manage:
     command: snap-openstack glance-manage
-    aliases:
-      - glance-manage
     plugs:
       - network