tests: make custom templates that use {whyunstable} terser

These templates demonstrate that {whyunstable} is fully template-friendly, but
they don't need to produce such long lines of output.

tests/test-obsolete-divergent.t

@@ -723,10 +723,10 b' Use scmutil.cleanupnodes API to create d'
 
   $ hg log -r 1a2a9b5b0030 -T '{whyunstable}\n'
   content-divergent: 4:70d5a63ca112 (draft) predecessor a178212c3433
-  $ hg log -r 1a2a9b5b0030 -T '{whyunstable%"{instability}:{divergentnodes} {reason} {node}\n"}'
-  content-divergent: 4:70d5a63ca112 (draft) predecessor a178212c3433c4e77b573f6011e29affb8aefa33
-  $ hg log -r 1a2a9b5b0030 -T '{whyunstable%"{instability}:{divergentnodes % " {node} ({phase})"} {reason} {node}\n"}'
-  content-divergent: 70d5a63ca112acb3764bc1d7320ca90ea688d671 (draft) predecessor a178212c3433c4e77b573f6011e29affb8aefa33
+  $ hg log -r 1a2a9b5b0030 -T '{whyunstable % "{instability}:{divergentnodes} {reason} {node|shortest}\n"}'
+  content-divergent: 4:70d5a63ca112 (draft) predecessor a178
+  $ hg log -r 1a2a9b5b0030 -T '{whyunstable % "{instability}:{divergentnodes % " {node|shortest} ({phase})"} {reason} {node|shortest}\n"}'
+  content-divergent: 70d5 (draft) predecessor a178
 
 #if serve
 

tests/test-obsolete.t

@@ -1049,9 +1049,9 b' test whyunstable template keyword'
   $ hg log -r 50c51b361e60 -T '{whyunstable}\n'
   orphan: obsolete parent 3de5eca88c00
   phase-divergent: immutable predecessor 245bde4270cd
-  $ hg log -r 50c51b361e60 -T '{whyunstable%"{instability}: {reason} {node}\n"}'
-  orphan: obsolete parent 3de5eca88c00aa039da7399a220f4a5221faa585
-  phase-divergent: immutable predecessor 245bde4270cd1072a27757984f9cda8ba26f08ca
+  $ hg log -r 50c51b361e60 -T '{whyunstable % "{instability}: {reason} {node|shortest}\n"}'
+  orphan: obsolete parent 3de5
+  phase-divergent: immutable predecessor 245b
 
 #if serve