Improve check_backend()

[ChristianKuehnel]

I'm not happy with the interface of the check_backend() function:

• it should be static so you don't have to instantiate the class when checking.
• it should return True/False instead of throwing exceptions
• there should be a function available that returns the list of all available backends, so that you don't have to iterate and check manually.

[coveralls]

Coverage increased (+0.5%) to 86.102% when pulling 6c2648c6169ac867748588b43d6b72d2023b8de3 on ChristianKuehnel:check_backend into 0af1185abfbfe35ed2202b0ebab9e94a646efe4a on open-homeautomation:master.

[coveralls]

Coverage increased (+0.5%) to 86.102% when pulling 6c2648c6169ac867748588b43d6b72d2023b8de3 on ChristianKuehnel:check_backend into 0af1185abfbfe35ed2202b0ebab9e94a646efe4a on open-homeautomation:master.

[coveralls]

Coverage increased (+0.5%) to 86.102% when pulling 6c2648c6169ac867748588b43d6b72d2023b8de3 on ChristianKuehnel:check_backend into 0af1185abfbfe35ed2202b0ebab9e94a646efe4a on open-homeautomation:master.

[coveralls]

Coverage increased (+0.5%) to 86.102% when pulling c24c155686e0cee0519f74d63cd4544e2b6f0e0e on ChristianKuehnel:check_backend into 0af1185abfbfe35ed2202b0ebab9e94a646efe4a on open-homeautomation:master.

[coveralls]

Coverage increased (+0.8%) to 86.333% when pulling 73e3980b742cf61526a58a572f9d7b9f380c4757 on ChristianKuehnel:check_backend into 0af1185abfbfe35ed2202b0ebab9e94a646efe4a on open-homeautomation:master.

[coveralls]

Coverage increased (+0.8%) to 86.333% when pulling d73578c7d1c6ba3f8d8ed071371d6221087a210c on ChristianKuehnel:check_backend into 0af1185abfbfe35ed2202b0ebab9e94a646efe4a on open-homeautomation:master.

[coveralls]

Coverage increased (+0.8%) to 86.333% when pulling 39b4fbeb7ea24f8baf4537de384534665510c638 on ChristianKuehnel:check_backend into 0af1185abfbfe35ed2202b0ebab9e94a646efe4a on open-homeautomation:master.

[coveralls]

Coverage increased (+0.8%) to 86.333% when pulling 5f21956959bd031a8be90d468491af8a403565b3 on ChristianKuehnel:check_backend into 0af1185abfbfe35ed2202b0ebab9e94a646efe4a on open-homeautomation:master.

[coveralls]

Coverage increased (+0.8%) to 86.333% when pulling 5f21956959bd031a8be90d468491af8a403565b3 on ChristianKuehnel:check_backend into 0af1185abfbfe35ed2202b0ebab9e94a646efe4a on open-homeautomation:master.

[coveralls]

Coverage increased (+0.8%) to 86.333% when pulling 5f21956959bd031a8be90d468491af8a403565b3 on ChristianKuehnel:check_backend into 0af1185abfbfe35ed2202b0ebab9e94a646efe4a on open-homeautomation:master.

[coveralls]

Coverage increased (+0.8%) to 86.333% when pulling 5f21956959bd031a8be90d468491af8a403565b3 on ChristianKuehnel:check_backend into 0af1185abfbfe35ed2202b0ebab9e94a646efe4a on open-homeautomation:master.