Every meta data service should return bytes only for these capabilities:
* get_content
* get_user_data
While `_get_meta_data` and any other method derrived from it
(including public keys, certificates etc.) should return homogeneous
data types and only strings, not bytes.
The decoding procedure is handled at its roots, not in the plugins
and is done by only using `encoding.get_as_string` function.
Fixed bugs:
* invalid certificate splitting under maas service which usually
generated an extra invalid certificate (empty string + footer)
* text operations on bytes in maas and cloudstack (split, comparing)
* multiple types for certificates (now only strings)
* not receiving bytes from opennebula service when using `get_user_data`
(which leads to crash under later processing through io.BytesIO)
* erroneous certificate parsing/stripping/replacing under x509 importing
(footer remains, not all possible EOLs replaced as it should)
Also added new and refined actual misleading unittests.
Change-Id: I704c43f5f784458a881293d761a21e62aed85732
ae15fee086