Remove putAll usage

[mccartney]

What:
Minor refactoring.
Avoid the usage of putAll method.

Why:
To avoid the compilation error:

src/main/scala/com/sumologic/sumobot/brain/S3Brain.scala:82:11: ambiguous reference to overloaded definition,
both method putAll in class Properties of type (x$1: java.util.Map[_, _])Unit
and  method putAll in class Hashtable of type (x$1: java.util.Map[_ <: Object, _ <: Object])Unit
match argument types (java.util.Map[String,String])
one error found

using some Java versions.

Context: scala/bug#10418