Skipped tests shouldn't be failures

Summary: If we skip a test, we shouldn't mark `make check` as failure. This fixes travis CI test.

Test Plan: Travis CI

Reviewers: noetzli, sdong

Reviewed By: sdong

Subscribers: dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D47031

db/prefix_test.cc

@@ -8,8 +8,8 @@
 #ifndef GFLAGS
 #include <cstdio>
 int main() {
-  fprintf(stderr, "Please install gflags to run rocksdb tools\n");
-  return 1;
+  fprintf(stderr, "Please install gflags to run this test... Skipping...\n");
+  return 0;
 }
 #else
 

util/bloom_test.cc

@@ -10,8 +10,8 @@
 #ifndef GFLAGS
 #include <cstdio>
 int main() {
-  fprintf(stderr, "Please install gflags to run rocksdb tools\n");
-  return 1;
+  fprintf(stderr, "Please install gflags to run this test... Skipping...\n");
+  return 0;
 }
 #else
 

util/dynamic_bloom_test.cc

@@ -6,8 +6,8 @@
 #ifndef GFLAGS
 #include <cstdio>
 int main() {
-  fprintf(stderr, "Please install gflags to run rocksdb tools\n");
-  return 1;
+  fprintf(stderr, "Please install gflags to run this test... Skipping...\n");
+  return 0;
 }
 #else