test-skeleton: increase default TIMEOUT to 20 seconds

The vast majority of timeouts I've seen w/glibc tests are due to:
 - slow system (e.g. <1 GHz cpu)
 - loaded system (e.g. lots of parallelism)
Even then, I've seen timeouts on system I don't generally consider
slow, or even loaded, and considering TIMEOUT is set to <=10 in ~60
tests (and <=20 in ~75 tests), it seems I'm not alone.  I've just
gotten in the habit of doing `export TIMEOUTFACTOR=10` on all my
setups.

In the edge case where there is a bug in the test and the timeout is
hit, I think we all agree that's either a problem with the test or a
real bug in the library somewhere.  In either case, the incident rate
should be low, so catering to that seems like the wrong trade-off.

Other developers too usually set large timeout factors.  Increase the
default to 20 seconds to match reality.

ChangeLog

@@ -1,3 +1,7 @@
+2016-02-19  Mike Frysinger  <vapier@gentoo.org>
+
+	* test-skeleton.c (TIMEOUT): Change to 20 and adjust comment.
+
 2016-02-19  Carlos O'Donell  <carlos@systemhalted.org>
 
 	* nptl/allocatestack.c (allocate_stack): Declare new stackaddr,

test-skeleton.c

@@ -46,8 +46,9 @@
 #endif
 
 #ifndef TIMEOUT
-  /* Default timeout is two seconds.  */
-# define TIMEOUT 2
+  /* Default timeout is twenty seconds.  Tests should normally complete faster
+     than this, but if they don't, that's abnormal (a bug) anyways.  */
+# define TIMEOUT 20
 #endif
 
 #define OPT_DIRECT 1000