[builder] make retries configurable

lib/omnibus/builder.rb

@@ -213,6 +213,10 @@ def execute_proc(cmd)
       raise
     end
 
+    def build_retries
+      Omnibus.config[:build_retries]
+    end
+
     def execute_sh(cmd)
       retries ||= 0
       shell = nil
@@ -243,10 +247,11 @@ def execute_sh(cmd)
         shell.error!
       end
     rescue Exception => e
+      raise if build_retries.nil? || build_retries == 0
       # Getting lots of errors from github, particularly with erlang/rebar
       # projects fetching tons of deps via git all the time. This isn't a
       # particularly elegant way to solve that problem. But it should work.
-      if retries >= 3
+      if retries >= build_retries
         ErrorReporter.new(e, self).explain("Failed to build #{name} while running `#{cmd_string}` with #{cmd_opts_for_display}")
         raise
       else

lib/omnibus/config.rb

@@ -197,6 +197,13 @@ class Config
 
     # # @!endgroup
 
+    # @!group Build Control Parameters
+
+    # @! attribute [rw] build_retries
+    #
+    #   @return [Integer, nil]
+    build_retries 3
+
     # @!group Validation Methods
 
     # Asserts that the Config object is in a valid state.  If invalid