nmon_cleaner.sh schedule update to prevent unexpected reader duplications

[Guilhem Marchand]

• The current schedule of the metricator_cleaner.sh runs once per day, this does not allow preventing duplication of the metricator_reader.pl|.py processes in cases of unexpected issue affecting the process termination

• in normal circumstances, the reader process exits normally when the nmon binary process dies, in some unexpected situations, duplication of the process was reported by some users

• the task maintenance included in the metricator_cleaner.sh prevents this situation, at the condition that its runs often enough

• schedule will be changed to every 4 hours (14400 sec)

[Guilhem Marchand]

Fix Issue #8

→ <<cset 108823c93fcc>>