build: avoid confusing make with raw name 'undefine'

Make has a builtin operator 'undefine', and coupled with latest
automake.git, this test name ended up confusing make into thinking
the file name was meant to be used as the make operator.  Renaming
the file avoids the confusion.

* tests/undefine: Rename...
* tests/virsh-undefine: ...to this.
* tests/Makefile.am (test_scripts): Use new name.
Reported by Jim Meyering.

(cherry picked from commit a20f06d9)

tests/Makefile.am

@@ -178,12 +178,13 @@ test_scripts +=				\
 	read-bufsiz			\
 	read-non-seekable		\
 	start				\
-	undefine			\
 	vcpupin				\
 	virsh-all			\
 	virsh-optparse			\
 	virsh-schedinfo			\
-	virsh-synopsis
+	virsh-synopsis			\
+	virsh-undefine			\
+	$(NULL)
 
 test_programs += eventtest
 else
@@ -198,12 +199,13 @@ EXTRA_DIST += 				\
 	read-bufsiz			\
 	read-non-seekable		\
 	start				\
-	undefine			\
 	vcpupin				\
 	virsh-all			\
 	virsh-optparse			\
 	virsh-schedinfo			\
-	virsh-synopsis
+	virsh-synopsis			\
+	virsh-undefine			\
+	$(NULL)
 endif
 
 if WITH_SECDRIVER_APPARMOR