Add flags module

FileFlagSource reads flags from files in /etc/vespa/flags and is a component
that can be injected in host admin, config server, etc. A flag named foo
corresponds to filename foo.

In general a FlagSource manages:
 - Feature flags: A feature is either set (true/enabled) or otherwise false.
   Touching a file foo means the feature flag foo is set (true).
 - Value flags: Either a String or empty if not set. The String corresponds to
   the file content.

The plan is to make the config server another source of flags. A unified
FlagSource can merge the two sources with some priority and used in e.g. parts
of node-admin. In other parts one would only have access to the file source.

Defines various flag facades:
 - FeatureFlag: Used to test whether a feature has been enabled or not.
 - IntFlag
 - JacksonFlag: Deserializes JSON to Jackson class, or return default if unset.
 - LongFlag
 - OptionalJacksonFlag: Deserializes JSON to Jackson class, or empty if unset.
 - OptionalStringFlag
 - StringFlag

This is part of removing some of the last Chef recipes. Some minor tweaks have
been necessary as part of this and are included in this PR (test whether a
systemd service exists, task-friendly file deletion, allow capitalized letters
in YUM package name).

1 files changed, 9 insertions, 10 deletions

diff --git a/node-admin/src/main/java/com/yahoo/vespa/hosted/node/admin/task/util/file/UnixPath.java b/node-admin/src/main/java/com/yahoo/vespa/hosted/node/admin/task/util/file/UnixPath.java
index 4bd3aad3f52..1b927cfc682 100644
--- a/node-admin/src/main/java/com/yahoo/vespa/hosted/node/admin/task/util/file/UnixPath.java
+++ b/node-admin/src/main/java/com/yahoo/vespa/hosted/node/admin/task/util/file/UnixPath.java
@@ -49,16 +49,6 @@ public class UnixPath {
         return path;
     }
 
-    public boolean createParents() {
-        Path parent = path.getParent();
-        if (Files.isDirectory(parent)) {
-            return false;
-        }
-
-        uncheck(() -> Files.createDirectories(parent));
-        return true;
-    }
-
     public String readUtf8File() {
         return new String(readBytes(), StandardCharsets.UTF_8);
     }
@@ -141,6 +131,15 @@ public class UnixPath {
         return this;
     }
 
+    public UnixPath createParents() {
+        Path parent = path.getParent();
+        if (!Files.isDirectory(parent)) {
+            uncheck(() -> Files.createDirectories(parent));
+        }
+
+        return this;
+    }
+
     public UnixPath createDirectory(String permissions) {
         Set<PosixFilePermission> set = getPosixFilePermissionsFromString(permissions);
         FileAttribute<Set<PosixFilePermission>> attribute = PosixFilePermissions.asFileAttribute(set);