Fix lava-server manage addldapuser --username USER
Fix lava-server manage addldapuser --username USER

Attributes should be byte strings, while the python default now is to use
unicode strings (as we are importing unicode_literals).

Thanks-to: Christophe Guillon <christophe.guillon@st.com>

Change-Id: Ifa5bc31e32e46fe8fba0512c954cae21637627b8

Linaro/lava-server,Linaro/lava-server,Linaro/lava-server,Linaro/lava-server