redmine: Add OpenID Digest::HMAC fix

From Holger:
Digest: This seems a bit of the magic of ruby but I vaguely remember having seen this before. I have
either patched or backported a fix. In newer Ruby versions "Digest" has been deprecated. The diff to
"stock" openid 2.3.0 is:

Change-Id: Idaca479140846481372ad0e1bff741bb09010847
Related: OS#3081

redmine/Dockerfile

@@ -9,3 +9,6 @@ RUN	apt-get update && \
 
 COPY	redmine-issue-2047-svg-image-support.diff /tmp/redmine-issue-2047-svg-image-support.diff
 RUN	cd app && patch -p1 < /tmp/redmine-issue-2047-svg-image-support.diff
+
+COPY	redmine-openid-hmac-digest.diff /tmp/
+RUN	cd /usr/local/bundle/gems/ruby-openid-2.3.0 && patch -p0 < /tmp/redmine-openid-hmac-digest.diff

redmine/redmine-openid-hmac-digest.diff

@@ -0,0 +1,46 @@
+diff -Nurd lib/openid/cryptutil.rb
+/usr/local/lib/ruby/gems/2.3/gems/ruby-openid-2.3.0/lib/openid/cryptutil.rb
+--- lib/openid/cryptutil.rb     1970-01-01 00:00:00.000000000 +0000
++++ /usr/local/lib/ruby/gems/2.3/gems/ruby-openid-2.3.0/lib/openid/cryptutil.rb 2017-07-17
+18:25:45.146746571 +0000
+@@ -2,7 +2,7 @@
+ require "digest/sha1"
+ require "digest/sha2"
+ begin
+-  require "digest/hmac"
++  require "openssl"
+ rescue LoadError
+   begin
+     # Try loading the ruby-hmac files if they exist
+@@ -33,27 +33,19 @@
+     end
+
+     def CryptUtil.sha1(text)
+-      return Digest::SHA1.digest(text)
++      return OpenSSL::Digest.new('sha1').digest(text)
+     end
+
+     def CryptUtil.hmac_sha1(key, text)
+-      if Digest.const_defined? :HMAC
+-        Digest::HMAC.new(key,Digest::SHA1).update(text).digest
+-      else
+-        return HMAC::SHA1.digest(key, text)
+-      end
++      return OpenSSL::HMAC.digest('sha1', key, text)
+     end
+
+     def CryptUtil.sha256(text)
+-      return Digest::SHA256.digest(text)
++      return OpenSSL::Digest.new('sha256').digest(text)
+     end
+
+     def CryptUtil.hmac_sha256(key, text)
+-      if Digest.const_defined? :HMAC
+-        Digest::HMAC.new(key,Digest::SHA256).update(text).digest
+-      else
+-        return HMAC::SHA256.digest(key, text)
+-      end
++      return OpenSSL::HMAC.digest('sha256', key, text)
+     end
+
+     # Generate a random string of the given length, composed of the