Skip Database tests or make it more correct

[ktrace]

Installed gammu 1.38.5/1.40.1, builded with postgresql. But python-gammu 2.12 fail tests:

test_inject (test.test_smsd.SMSDDummyTest) ... Fri 2019/11/01 15:50:09 python-gammu[23837]: Using SQL service
Fri 2019/11/01 15:50:09 python-gammu[23837]: Configuring Gammu SMSD...
Fri 2019/11/01 15:50:09 python-gammu[23837]: SHM token: 0x103715e (17002846)
Fri 2019/11/01 15:50:09 python-gammu[23837]: Warning: No PIN code in /var/calculate/tmp/portage/dev-python/python-gammu-2.12/temp/tmployHVJ/.gammurc file
Fri 2019/11/01 15:50:09 python-gammu[23837]: CommTimeout=1, SendTimeout=30, ReceiveFrequency=15, ResetFrequency=0, HardResetFrequency=0
Fri 2019/11/01 15:50:09 python-gammu[23837]: checks: CheckSecurity=1, CheckBattery=1, CheckSignal=1, CheckNetwork=1
Fri 2019/11/01 15:50:09 python-gammu[23837]: mode: Send=1, Receive=1
Fri 2019/11/01 15:50:09 python-gammu[23837]: deliveryreport = no
Fri 2019/11/01 15:50:09 python-gammu[23837]: phoneid = 
Fri 2019/11/01 15:50:09 python-gammu[23837]: Unknown DB driver
ERROR

(twice)

======================================================================
ERROR: test_inject (test.test_smsd.SMSDDummyTest)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/var/calculate/tmp/portage/dev-python/python-gammu-2.12/work/python-gammu-2.12/test/test_smsd.py", line 91, in test_inject
    smsd = self.get_smsd()
  File "/var/calculate/tmp/portage/dev-python/python-gammu-2.12/work/python-gammu-2.12/test/test_smsd.py", line 85, in get_smsd
    return gammu.smsd.SMSD(self.config_name)
ERR_UNKNOWN: {'Text': u'Unknown error.', 'Code': 27, 'Where': 'SMSD_ReadConfig'}

(twice too)

FAILED (errors=2)
Test failed: <unittest.runner.TextTestResult run=50 errors=2 failures=0>
python-gammu: WARNING: Adding USSD to queue, position 0
Gammu version (1, 40, 0), SMSD DB version 17
Gammu version (1, 40, 0), SMSD DB version 17
Log filename is "stderr"
Gammu version (1, 40, 0), SMSD DB version 17
Log filename is "stderr"
error: Test failed: <unittest.runner.TextTestResult run=50 errors=2 failures=0>

With 1.38.5 same result. Perhaps it's not bug, but need explanations...