allow nvme, since virtualbox 6.0 allows it

Fix incorrect variable name galaxy_command

builder/linode: remove unused sshConfig() and associated import

common: Resuscitate Floppy Tests

builder/vmware: Remove Unused Test Helper Functions

common: remove unused test function getDirectory()

delete amazon import post-processor intermediary snapshots

builder/openstack: remove dead testConfig() function

Cleanup builder/amazon/common

Document duration strings better to avoid confusion

builder/amazon/common: remove dead test type and function mockEC2Conn_Modify_EBS.ModifyInstanceAttribute()

builder/amazon/common: remove dead test type and function mockEC2ConnSpot.DescribeSpotPriceHistory()

It is simply the best/simplest solution and trying to prevent users from passing and integer here would be like opening a can of worms. Because:

* we cannot make mapstructure validate our duration string ( with an UnmarshalJSON func etc.)
* we cannot make mapstructure spit a string instead of a duration and packer will decode-encode-decode config.
* the hcl2 generated code asks for a string, so this will be enforced by default.

Before this commit it was possible to set a duration using an integer or a float. Go's time.Duration is an int64 internally an mapstructure will take advantage of this and load the number as a int64 but `1` means one ns which is unexpected/confusing. To avoid confusion and enforce readability this forces users to pass a string with a unit for a duration; ex "56s".

add insert_key option for toggling whether to add Vagrant's insecure key