Backport try_megabytes_to_bytes from EE

EE adds this method to Gitlab::Utils, which is also required by our
SimpleCov helper. This prevents us from injecting EE modules into
Gitlab::Utils, because the necessary bits for this are not yet in place.

To work around this we just backport try_megabytes_to_bytes, as there's
no particular reason to keep this in EE only.

lib/gitlab/utils.rb

@@ -104,7 +104,6 @@ module Gitlab
       nil
     end
 
-    # EE below
     def try_megabytes_to_bytes(size)
       Integer(size).megabytes
     rescue ArgumentError

spec/lib/gitlab/utils_spec.rb

@@ -213,4 +213,22 @@ describe Gitlab::Utils do
       expect(subject[:variables].first[:key]).to eq('VAR1')
     end
   end
+
+  describe '.try_megabytes_to_bytes' do
+    context 'when the size can be converted to megabytes' do
+      it 'returns the size in megabytes' do
+        size = described_class.try_megabytes_to_bytes(1)
+
+        expect(size).to eq(1.megabytes)
+      end
+    end
+
+    context 'when the size can not be converted to megabytes' do
+      it 'returns the input size' do
+        size = described_class.try_megabytes_to_bytes('foo')
+
+        expect(size).to eq('foo')
+      end
+    end
+  end
 end