WT-3959 Manage recovery timestamp via a new schema entry

[agorrod]

This branch was merged once, but introduced test failures, so I reverted.

[agorrod]

I've reproduced the failure once in about 30 minutes running 4 reproducers in parallel. The configuration I was using is:

../configure --enable-python --with-spinlock=pthread_adaptive --enable-strict && make -j12
export WIREDTIGER_CONFIG="checkpoint_sync=0,transaction_sync=(method=none)"
for i in `seq 100`; do ./test_timestamp_abort -h WT_TEST.2 -T 5 -t 20 || break ; done

i.e: a slightly longer runtime than the configuration that failed in Jenkins.

[agorrod]

It reproduced much faster running 20 in parallel:

#!/bin/bash
for j in `seq 100`; do
       	for i in `seq 20`; do
	       	./test_timestamp_abort -h WT_TEST.$i -T 5 -t 10 || break > run.$i.out &
       	done
       	wait
done