Add support for vagrant-docker (#389)

* clean trailing ws in Vagrantfile and util/avr_setup.sh

* replace triple quotes with heredoc.

Ruby doesn't have triple quotes; that's a Python thing. This was just being
parsed as multiple strings concatenated.

* add docker support to Vagrantfile

* make wants to find dfu-programmer in vagrant guest

util/avr_setup.sh

@@ -38,8 +38,9 @@ elif [[ -n "$(type -P apt-get)" ]]; then
     gcc-avr \
     binutils-avr \
     avr-libc \
+    dfu-programmer \
     dfu-util
-  
+
 elif [[ -n "$(type -P yum)" ]]; then
   # Fedora, CentOS or RHEL and derivatives
   yum -y makecache && yum -y update
@@ -55,6 +56,7 @@ elif [[ -n "$(type -P yum)" ]]; then
     avr-binutils \
     avr-gcc \
     avr-libc \
+    dfu-programmer \
     dfu-util
 
 elif [[ -n "$(type -P zypper)" ]]; then