gst-client-1.0 in interactive mode leaks connections

[clogwog]

reproducible:

gstd --tcp-max-threads 1
gst-client-1.0
gstd> list_pipelines  (works)
gstd> list_pipelines (hangs)

then

gstd --tcp-max-threads 2
gst-client-1.0
gstd> list_pipelines  (works)
gstd> list_pipelines  (works)
gstd> list_pipelines (hangs)

working on a PR