HPCC-8537 Skip title line when parsing space usages in preflight

Preflight result contains a Space Usage title line 'SpaceUsedAndFree'
indicating the section. The existing EclWatch Preflight function tries
to parse the line and generates a log line 'Invalid storage information
on x.x.x.x: ---SpaceUsedAndFree---', which confuses the log user. The
code in this fix skips the title line when parsing the preflight result.

Signed-off-by: Kevin Wang <kevin.wang@lexisnexis.com>