plainbox:decorators: correct docstring

Signed-off-by: Zygmunt Krynicki <zygmunt.krynicki@canonical.com>
plainbox:decorators: fix PEP-8 issue

Signed-off-by: Zygmunt Krynicki <zygmunt.krynicki@canonical.com>
plainbox:decorators: document @raises UndocumentedException behavior

Signed-off-by: Zygmunt Krynicki <zygmunt.krynicki@canonical.com>
plainbox:decorators: add tests for UndocumentedError and no docstring

Signed-off-by: Zygmunt Krynicki <zygmunt.krynicki@canonical.com>
plainbox:decorators: remove needless whitespace

Signed-off-by: Zygmunt Krynicki <zygmunt.krynicki@canonical.com>
"automatic merge of lp:~zkrynicki/checkbox/decorators/ by tarmac [r=kissiel][bug=][author=zkrynicki]"