test_nodes.vty: Since libosmocore 1.0.0, we only have one space

The output of "logging level" was wrongly indented with two speaces, and
in commit 0d67f483e2d240089105a4d241cb8c9085e245af of libosmocore, first
released as part of libosmcoore-1.0.0 it was fixed.

This makes "make check" pass against libosmocore-1.0.0, but not against
earlier releases.

Change-Id: I2cc12b3f0df19d9055022db41f7f3f2789bd19c6