Trims whitespaces in PMA_HOSTS, PMA_PORTS and PMA_VERBOSES

[deeky666]

I encountered a problem when configuring hosts via yaml multiline:

environment:
    PMA_HOSTS: >
        host_a,
        host_b,
        host_c

This config resolves to PMA_HOSTS=host_a, host_b, host_c which leads to not being able to login to host_b and host_c because of leading whitespaces.

It would be really useful to be able to list hosts in multiple lines for readability and also version control diffing.

Therefore this patch simply trims each value in PMA_HOSTS, PMA_PORTS and PMA_VERBOSES.

[nijel]

Merged, thanks for your contribution!

[deeky666]

Thanks for merging!