{pxe|health}: Reporting git hash during boot

If edeploy pxe or health initrd got built on top of a git repo, let's
report the version during the boot.

This could avoid searching to solve already solved bugs... sometimes
only the ramfs didn't got rebuilt or not properly booted.

A typical output looks like:

 Info: Probing ipmi_devintf failed
 Info: Added fake IPMI device
 Required kernel modules for 3.2.0-4-amd64 x86_64 are : ata_piix,
 piix4_smbus, virtio-pci,
 Running eDeploy with git hash = 718aa6438dade62354c809b630a3171266054c41
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 Configuring system via server 10.0.2.2
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