BumbleBluetoothTests: Improve directConnectGattAfterClose

Reduce the flakyness of GattClientTest#directConnectGattAfterClose
by only reconnecting once (instead of 10 times) and ensuring the
second gatt connection disconnects before the end of the test.

Bug: 322506814
Flag: TEST_ONLY
Test: atest BumbleBluetoothTests:android.bluetooth.GattClientTest
Change-Id: I221291d49f6c14e3e3652288f35d4dcaa095415d