Read volume meta by sxc_cluster_listvolumes() if needed.

This reduces amount of cluster queries for sxls -l sx://cluster/
locking semantics
http api entries for lock/unlock
jlock job
unify job stubs
Add test for ?volumeList&volumeMeta
Escape string printed by sxls.

Replace control chars by '?'.
Apply replacing for sxi_log_call() and sxc_geterrmsg().
fix acl test in make check

This fixes the heisenbug on FreeBSD: changing volume ACLs is not instant:
it is a job that has to be waited for.
The script didn't wait, so it was just a coincidence that the acl change
was "fast enough" most of the time.
Control number of active connections globally and per host.

Default limit for active connections is defined as
MAX_ACTIVE_CONNECTIONS and set to 5.
Default number of active connections with each host is defined as
MAX_ACTIVE_PER_HOST and set to 2.
Both global and per-host limits can be set at runtime.

Add possibility to change those limits in sxcp command with hidden
command line arguments (see sxcp --full-help).