Update the gate hooks to install proper docker package
Update the gate hooks to install proper docker package

The way gate_hook.sh tries to find the proper package to install is
sub-optimal, and misses in case there is another package containing the
package name as a substring.
Updating the file to work the same way as in [1].

[1] https://github.com/openstack/neutron-dynamic-routing/commit/c27bb1f190a60d201d616bebd42c60dae6afa545

Change-Id: I726f993ef9d593f13abef55fca6cc2c0a2d353c7

openstack/dragonflow,openstack/dragonflow,openstack/dragonflow