Connect battery service only when it's available

As we tried to connect to the battery service
whenever a BLE device is connected, BatteryService
logs errors when a BLE device not supporting BAS
is connected.
This CL checks the availability first to prevent
logging errors

Tag: #feature
Bug: 235566393
Test: manually confirmed BAS works and no error for
devices not having BAS.

Change-Id: I87698e3838dce63e05fb69c6d2624f4219edb149