providers/alicloud: shouldn't access p.Service in GetConfig()

[cofyc]

fixes #681

why

p.Service is not initialized when we call GetConfig here:

https://github.com/GoogleCloudPlatform/terraformer/blob/master/cmd/import.go#L113-L116

and it's better to use p.profile field which is initialized in Init():

terraformer/providers/alicloud/alicloud_provider.go

Lines 112 to 116 in b9a6ae6

	func (p *AliCloudProvider) Init(args []string) error {
	p.region = args[0]
	p.profile = args[1]
	return nil
	}

$ terraformer import alicloud --resources=* --profile=<xxx> --regions cn-hangzhou
2020/12/01 20:17:17 alicloud importing region cn-hangzhou
2020/12/01 20:17:17 Attempting an import of ALL resources in alicloud
2020/12/01 20:17:17 provider name: alicloud
panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x18 pc=0x1998da1]

goroutine 1 [running]:
github.com/GoogleCloudPlatform/terraformer/providers/alicloud.(*AliCloudProvider).GetConfig(0xc000786730, 0x7471d77, 0x8, 0x1, 0x1)
	/data/go/src/github.com/GoogleCloudPlatform/terraformer/providers/alicloud/alicloud_provider.go:34 +0x41
github.com/GoogleCloudPlatform/terraformer/cmd.Import(0x7ce8ce0, 0xc000786730, 0xc000b3f700, 0xb, 0x10, 0xc0000787b0, 0x2a, 0x7474e4b, 0x9, 0x746c083, ...)
	/data/go/src/github.com/GoogleCloudPlatform/terraformer/cmd/import.go:97 +0x2e7
...

[cofyc]

@sergeylanzman WDYT?