pynipap: new prefix from-pool seems not to take pool's default type

[andris]

Thanks for the great tool that is NIPAP! Just trying some integration with my own tools via pynipap.

According to the documentation, calling save() on a new prefix calls http://nipap.readthedocs.io/en/latest/nipap.html#nipap.backend.Nipap.add_prefix

According to the add_prefix documentation: 'the type key can be omitted and the prefix type will then be set to the pools default prefix type'

However, if i try to allocate a new prefix from an existing pool that has default type 'assignment', save() fails with 'pynipap.NipapValueError: Unknown prefix type'. If i manually set the prefixes type prior to saving

example without explicitly setting type of new prefix.

testPrefix = Prefix()
testPrefix.description = "testPrefix"
testPrefix.save({ 'from-pool': samplePool, 'family': 4})

fails with pynipap.NipapValueError: Unknown prefix type

example with explicitly setting type of new prefix

testPrefix = Prefix()
testPrefix.description = "testPrefix"
testPrefix.type = "assignment"
testPrefix.save({ 'from-pool': samplePool, 'family': 4})

succeeds