[sdk-manage] more quiet zypper

Signed-off-by: Juha Kallioinen <juha.kallioinen@jolla.com>
[mb2] minor performance optimizations

Signed-off-by: Juha Kallioinen <juha.kallioinen@jolla.com>
[mb2] avoid piping to processes

Signed-off-by: Juha Kallioinen <juha.kallioinen@jolla.com>
[mb2] only use builtin test expression

Signed-off-by: Juha Kallioinen <juha.kallioinen@jolla.com>