common: introduce common module

This module's purpose is to provide shared functions, constants, etc.
for storage plugins and storage-related operations.

It starts out with a align_size_up() function, that will (initially)
be used for volume import.

[FE: start out with a different function for my use case
     fixup Makefile]

Originally-by: Max Carrara <m.carrara@proxmox.com>
Signed-off-by: Fiona Ebner <f.ebner@proxmox.com>

src/PVE/Storage/Common/Makefile

@@ -0,0 +1,6 @@
+SOURCES = \
+
+
+.PHONY: install
+install:
+	for i in ${SOURCES}; do install -D -m 0644 $$i ${DESTDIR}${PERLDIR}/PVE/Storage/Common/$$i; done