Decrease concurrency for webrequest log verification

Due to switching from plain partition adding to checking for
duplicates/holes the workflow is no longer that cheap, and we hence
limit the concurrency.

Change-Id: Idfcaf8bb021b13a418e1fd7dec1007188d1ff2e6
Increase timeout for webrequest log verification

The cluster's default of 2 hours is too short to allow automatic
handling of transient issues.

Change-Id: Ic688bfa83b61f18fac5aa581dd390cd41cea7f15
Document XML tag placement convention for multi-line element values

See line 33 of

  https://gerrit.wikimedia.org/r/#/c/143486/5/oozie/webrequest/compute_sequence_stats/coordinator.xml

Change-Id: I3a3932a13d54e7e3c971244cfd351658381f02f4
Merge changes Ic688bfa8,Idfcaf8bb

* changes:
  Increase timeout for webrequest log verification
  Decrease concurrency for webrequest log verification
Merge "Document XML tag placement convention for multi-line element values"