webadmin: shorten columns on Network->Hosts sub tab

Shortened-
1) Column Network Device

Shortened and remaned-
1) "Network Device Speed"->"Speed (Mbps)"
2) "Network Device Rx (Mbps)"->"Receive (Mbps)"
3) "Network Device Tx (Mbps)"->"Transmit (Mbps)"

Change-Id: I5e23d51e76ac0aba9b4b253fa04b03a0c8cb5da7
Bug-Url: https://bugzilla.redhat.com/1108062
Signed-off-by: Alona Kaplan <alkaplan@redhat.com>