Ensure the DUT is bondable during test

CTS Verifier Bluetooth Secure Client testcase
may fail if the DUT is not in a bondable state.
Bondable mode may be restricted in some devices,
such as only when the device is also discoverable.

To accommodate all devices, the scan mode as should
be set to SCAN_MODE_CONNECTABLE_DISOVERABLE before
proceeding with the Bluetooth Secure Client test.

Test: CTS Verifier > Bluetooth > Secure Client Test

Bug: 176501682
Tag: #compatibility
Sponsor: velazcod@
Change-Id: I12dca55e8cc70041052a936e43c0975f09f09c94