Rename pxe_template_dir setting to boot_loader_conf_template_dir

PXE refers to DHCP+TFTP. This template directory only contains
boot loader configuration templates, so setting name should reflect
that more clearly.
Rename source/dest boot loader configuration templates directories

PXE refers to DHCP+TFTP. This template directory only contains
boot loader configuration templates, so directory name should
reflect that more clearly.
Merge pull request #1215 from alanoe/alanoe/rename_boot_loader_conf_templates_dir

alanoe/rename boot loader conf templates dir