CA-115742: VM name and description change not allowed via XenCenter for ...

...VM Admin - FIXED

The error has been caused by the shadow multiplier field on Advanced Settings page: XenCenter thinks that the values has changed, and tries to save it, but this is not allowed for VM Admin users.
The solution is:
- use -1 as the signal value for unparseable string, instead of 1.0, which is actually a valid value;
- display the existing value without formatting it to 2 deciaml places;
Also corrected the validation function, as the shadow multiplier has to be greater than or equal to 1, not 0.1.

Signed-off-by: Mihaela Stoica <mihaela.stoica@citrix.com>