add 'show subscriber' command, alias for 'subscriber ... show'

When I wrote the osmo-hlr subscriber command, I failed to heed the common
'show foo' scheme and instead created a 'subscriber [...] show' command.
Relieve that weirdness by creating an alias that has 'show' at the start.

Arrange string macros so that the 'show subscriber' cmd doesn't end in a space
(the SUBSCR macro ends in a space ' ' to implicitly include the space to
commands like 'create', 'show', 'update').

Add the new command to test_nodes.vty and test_subscriber.vty.

Change-Id: I01ce9b0868302d40ed05c6a588316a194d6071e4
diff --git a/tests/test_subscriber.vty b/tests/test_subscriber.vty
index 2da455f..c22f2df 100644
--- a/tests/test_subscriber.vty
+++ b/tests/test_subscriber.vty
@@ -3,6 +3,7 @@
 OsmoHLR# list
 ...
   subscriber (imsi|msisdn|id) IDENT show
+  show subscriber (imsi|msisdn|id) IDENT
   subscriber imsi IDENT create
   subscriber (imsi|msisdn|id) IDENT delete
   subscriber (imsi|msisdn|id) IDENT update msisdn MSISDN
@@ -33,6 +34,13 @@
 OsmoHLR# subscriber msisdn 12345 show
 % No subscriber for msisdn = '12345'
 
+OsmoHLR# show subscriber imsi 123456789023000
+% No subscriber for imsi = '123456789023000'
+OsmoHLR# show subscriber id 1
+% No subscriber for id = '1'
+OsmoHLR# show subscriber msisdn 12345
+% No subscriber for msisdn = '12345'
+
 OsmoHLR# subscriber imsi 1234567890230001 create
 % Not a valid IMSI: 1234567890230001
 OsmoHLR# subscriber imsi 12345678902300x create