Add support for environment variable substition for ADD and COPY resources

Supports the case where the name of the file is supposed to be resolved using an
environment variable.

ENV VAR sub

ADD files/$VAR.dat /$VAR.dat
ADD files/${VAR}.dat /${VAR}.dat

In both cases the VAR is substituted for sub.

This allows the tar file creation process to capture the real source file.
Add extra parameters to the DockerClient constructor's

The defaults remain 10 seconds for the read time out and to enable the
LoggingFilter.

Allows the caller to change the read time out and to disable the LoggingFilter

For large images the logging filter spam's the console with the binary data that
is being transferred.

This new setting allows it to be turned off.
Add new unit test case for ENV substitution
Merge pull request #16 from mocleiri/build-image-improvements

Build image improvements