euci: integrace *_default methods to get method

This is much more versatile and compact syntax. You can optionally set
default keywords argument and that gives you behavior where
UciExceptionNotFound is never thrown out.
This also adds tests for defaults.
1 job for get_t in 18 seconds (queued for 4 seconds)
Status Job ID Name Coverage
  Test
passed #268462
unittests

00:00:18