S3: Add support for custom apiserver

By setting the `hostname` value for a s3 backend, you can configure
lfs to use a custom s3-compatible apiserver.

Change-Id: I8f98b8171234959df008e871c91e44fdd039431c

src/main/java/com/googlesource/gerrit/plugins/lfs/s3/S3LargeFileRepository.java

diff --git a/src/main/java/com/googlesource/gerrit/plugins/lfs/s3/S3LargeFileRepository.java b/src/main/java/com/googlesource/gerrit/plugins/lfs/s3/S3LargeFileRepository.java
index a10242a..e10450c 100644
--- a/src/main/java/com/googlesource/gerrit/plugins/lfs/s3/S3LargeFileRepository.java
+++ b/src/main/java/com/googlesource/gerrit/plugins/lfs/s3/S3LargeFileRepository.java
@@ -15,6 +15,7 @@
 package com.googlesource.gerrit.plugins.lfs.s3;
 
 import com.google.common.base.MoreObjects;
+import com.google.common.base.Strings;
 import com.google.inject.Inject;
 import com.google.inject.assistedinject.Assisted;
 import com.googlesource.gerrit.plugins.lfs.LfsBackend;
@@ -35,6 +36,7 @@
 
   private static S3Config getS3Config(LfsGlobalConfig config, LfsBackend backendConfig) {
     String section = backendConfig.type.name();
+    String hostname = config.getString(section, backendConfig.name, "hostname");
     String region = config.getString(section, backendConfig.name, "region");
     String bucket = config.getString(section, backendConfig.name, "bucket");
     String storageClass =
@@ -47,6 +49,12 @@
     String accessKey = config.getString(section, backendConfig.name, "accessKey");
     String secretKey = config.getString(section, backendConfig.name, "secretKey");
 
+    if (!Strings.isNullOrEmpty(hostname)) {
+      return new S3Config(
+          hostname, region, bucket, storageClass, accessKey, secretKey, expirationSeconds,
+          disableSslVerify);
+    }
+
     return new S3Config(
         region, bucket, storageClass, accessKey, secretKey, expirationSeconds, disableSslVerify);
   }

src/main/resources/Documentation/config.md

diff --git a/src/main/resources/Documentation/config.md b/src/main/resources/Documentation/config.md
index 3013f5c..383cb9b 100644
--- a/src/main/resources/Documentation/config.md
+++ b/src/main/resources/Documentation/config.md
@@ -154,6 +154,11 @@
 
 The following configuration options are only used when the backend is `s3`.
 
+s3.hostname
+: Custom hostname for the S3 API server. This will allow for easier local testing
+of gerrit instances with lfs storage and for the utilization of custom storage
+solutions. If not specified, lfs will use AWS as the backend.
+
 s3.region
 : [Amazon region](http://docs.aws.amazon.com/AWSEC2/latest/UserGuide/using-regions-availability-zones.html#concepts-available-regions)
 the S3 storage bucket is residing in.