itest: add icase to node log filename + restart nodes before each icase

This commit adds the icase name to the log filename, to make it simpler
to find problematic tests. Additionally after this commit we'll restart
Alice and Bob (the base harness nodes) before each icase to start with a
clean state.

.gitignore

@@ -32,8 +32,7 @@ _testmain.go
 /lncli-itest
 
 # Integration test log files
-lntest/itest/output*.log
-lntest/itest/pprof*.log
+lntest/itest/*.log
 lntest/itest/.backendlogs
 lntest/itest/.minerlogs
 lntest/itest/lnd-itest
@@ -73,4 +72,4 @@ profile.tmp
 .vscode
 
 # Coverage test
-coverage.txt
+coverage.txt